AB0926 ENTHESITIS OF THE HAND IS A DOMINANT LESION IN PSORIATIC ARTHRITIS AND MAY HELP DISTINGUISH IT FROM RHEUMATOID ARTHRITIS: CASE-CONTROL, SINGLE-CENTRE, ULTRASOUND STUDY
Authors: D. Esperança Almeida, A. M. Gomes Correia, E. Costa, J. Neves, J. Silva, A. R. Ribeiro, M. Cerqueira
Journal: Annals of the Rheumatic Diseases (2022)

Background Enthesitis is the hallmark of psoriatic arthritis (PsA) and may assist in distinguishing PsA from other forms of arthritis (1,2). Its clinical evaluation is hampered by lack of specificity of physical examination (3). Ultrasound (US) may provide information about its presence and response to treatment. Although some previous works have shown that enthesitis of the hand is important in PsA (4), most US studies and scores focused on greater size entheses. Objectives To explore the prevalence of enthesitis of the hand in PsA patients as evaluated by US, and compare it with other inflammatory arthritides, namely rheumatoid arthritis (RA). Methods Cross-sectional study in which consecutive patients with PsA and RA were recruited for an US protocol evaluating 4 entheses of the hand including: 1. measurement of the extensor digitorum tendon central slip at its insertion at the middle phalanx of the 2 nd and 3 rd finger bilaterally; 2. search for the presence of power-Doppler (PD) sign; 3. identification of structural lesions. Linear regression models were built to test if diagnosis (PsA vs RA) explained part of the variance of the thickness of tendons insertion while controlling possible influences of age, type of work and body surface area. A ROC curve was built to find a mean thickness cut-off allowing distinction between PsA and RA. The prevalence of PD sign and structural lesions of the entheses was compared between groups. Results Fifty-eight patients were recruited (29 with PsA and 29 with RA) and a total of 232 entheses were evaluated. Mean thickness of the interest entheses was superior in PsA patients compared to RA patients (2 nd finger – 0.96 ± 0.16mm vs. 0.74 ± 0.09mm; 3 rd finger – 0.96 ± 0.20mm vs. 0.76 ± 0.11mm). Linear regression models including diagnosis and potential confounders significantly explained mean thickness of both entheses (2 nd finger – R 2 =0.56, p&lt;.001; 3 rd finger – R 2 =0.41, p&lt;.001), with the diagnosis group being the most important predictor (Table 1). ROC curve (AUC 0.897, p&lt;.001) showed a cut-off value of 0.925mm for the mean of the 4 entheses had a specificity of 93.1% for the identification of PsA patients. Table 1. Multiple linear regression models explaining thickness of the entheses. 2 nd finger (mean of both sides) 3 rd finger (mean of both sides) Linear regression model R 2 =0.56p&lt;.001*** R 2 =0.39p&lt;.001*** Diagnosis (PsA vs RA) β=0.587; B=0.203mmp&lt;.001*** β=0.483; B = 0.182mmp&lt;.001*** In our sample, 8 (3.5%) entheses had a measured thickness above mean + 2 SD, all belonging to PsA patients; 6 (75%) had signs of ongoing inflammatory process as proved by the presence of PD sign (Figure 1). Regarding structural lesions, enthesophytes or bone irregularities/erosions were found in 13.8% of PsA entheses, which compared to 1.7% of RA entheses. Figure 1. Enthesitis of the central slip of extensor digitorum of the 3rd finger in a patient with PsA: swelling of the 3rd proximal interphalangeal joint (A) due to inflammatory process originating in the enthesis, with no signs of synovitis, as evaluated by US (B). Conclusion This work reinforces enthesitis as a key lesion in PsA. It also shows enthesitis occurs significantly in small entheses, like the ones of the hand and that, in some instances, it may be the dominant lesion in a swollen joint. US may be valuable for establishing a diagnosis in the setting of inflammatory arthritis of unknown etiology. References [1]Mease P. Enthesitis in psoriatic arthritis (Part 3): clinical assessment and management. Rheumatology. 2020 Mar 1;59(Supplement_1):i21–8. [2]Sapundzhieva T, Karalilova R, Batalov A. Hand ultrasound patterns in rheumatoid and psoriatic arthritis: the role of ultrasound in the differential diagnosis. Rheumatol Int. 2020 Jun;40(6):837–48. [3]Kaeley GS. Enthesitis in psoriatic arthritis (Part 2): imaging. Rheumatology. 2020 Mar 1;59(Supplement_1):i15–20. [4]Smerilli G, Di Matteo A, Cipolletta E, Grassi W, Filippucci E. Enthesitis in Psoriatic Arthritis, the Sonographic Perspective. Curr Rheumatol Rep. 2021 Sep;23(9):75. Disclosure of Interests None declared